[PATCH] mm: Handle 0 flags in _calc_vm_trans() macro

[Jan Kara <jack@suse.cz>]

_calc_vm_trans() does not handle the situation when some of the passed
flags are 0 (which can happen if these VM flags do not make sense for
the architecture). Improve the _calc_vm_trans() macro to return 0 in
such situation. Since all passed flags are constant, this does not add
any runtime overhead.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 include/linux/mman.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Dan, can you please prepend this patch before my series so that we don't
break bisectability? This fixes the reported problem for me when arch
does not define MAP_SYNC. Thanks!

diff --git a/include/linux/mman.h b/include/linux/mman.h
index 8f7cc87828e6..3427bf3daef5 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -105,8 +105,9 @@ static inline bool arch_validate_prot(unsigned long prot)
  * ("bit1" and "bit2" must be single bits)
  */
 #define _calc_vm_trans(x, bit1, bit2) \
+  ((!(bit1) || !(bit2)) ? 0 : \
   ((bit1) <= (bit2) ? ((x) & (bit1)) * ((bit2) / (bit1)) \
-   : ((x) & (bit1)) / ((bit1) / (bit2)))
+   : ((x) & (bit1)) / ((bit1) / (bit2))))
 
 /*
  * Combine the mmap "prot" argument into "vm_flags" used internally.
-- 
2.12.3

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